The present invention relates to a transmission for a vehicle and, more particularly, to a synchronizer to be used in a manual transmission.
Here will be described a fundamental structure of a synchronizer to be used in a manual transmission for a vehicle. FIG. 7 shows a single cone type synchronizer, as disclosed in JPU No. 115221/1991. To a rotating shaft 1, there is splined a clutch hub 2. Across this clutch hub 2, there are rotatably arranged gears 3 and 4 to be synchronized. To the portions of these synchronized gears 3 and 4, as located at the side of the clutch hub 2, there are splined spline pieces 5 and 6. These spline pieces 5 and 6 are extended toward the clutch hub 2 to form boss portions. These boss portions are formed on their outer circumferences with taper cone portions 7 and 8, which are so fitted synchronizer rings 9 and 10 that they can move in the axial directions by a predetermined distance. Moreover, the clutch hub 2 has its outer circumference engaged by a hub sleeve 11 which is allowed to move only in the axial directions. This hub sleeve 11 has its inner circumference chamfered at its two end portions, and each of the synchronizer rings 9 and 10 also as its outer circumference chamfered. Moreover, each of the spline pieces 8 and 6 has its outer circumference splined to engage with the hub sleeve 11.
In the synchronizer thus constructed, as the hub sleeve 11 is moved toward one of the synchronized gears 3 and 4, the synchronizer rings 9 and 10 are accordingly moved toward the spline pieces 5 and 6 by the actions of (not-shown) keys. As a result, the synchronizer rings 9 and 10 are brought into engagement with the spline pieces 5 and 6 by the taper cone portions 7 and 8 so that they are synchronized to rotate. After the chamfers of the hub sleeve 11 and the chamfers of the synchronizer rings 9 and 10 have come into contact, the hub sleeve 11 is further moved. Then, the hub sleeve 11 advances while riding over the chamfers of the synchronizer rings 9 and 10 until it comes into engagement with the splines of the spline pieces 5 and 6.
The synchronizer rings 9 and 10 in the synchronizer acts to bring the hub sleeve 11 into engagement with the spline pieces 5 and 6 at the sides of the synchronized gears 8 and 4. Either in a neutral state, as shown in FIG. 7, or in the state in which a predetermined gear state is set by the not-shown gears, the synchronizer rings 9 and 10 are rotating together with the clutch hub 2. In case, however, no force is active to move the synchronizer rings 9 and 10 toward the clutch hub 2, the synchronizer rings 9 and 10 may come into engagement with the spline pieces 5 and 6 through the taper cone portions 7 and 8. In this state, the synchronizer rings 9 and 10 are rotating with the clutch hub 2, whereas the spline pieces 5 and 6 are rotating at a different velocity together with the synchronized gears 8 and 4. A slip is caused at the taper cone portions 7 and 8 to establish a sliding friction. This friction establishes a drag torque to cause a power loss and a temperature rise in the lubricating oil thereby to shorten the lifetime of the synchronizer rings. Due to a stick slip at the contacting time, moreover, the synchronizer rings bounce to make a noise (i.e., the so-called "chatter").
In the synchronizer of the prior art shown in FIG. 7, therefore, that portion of the clutch hub 2, which engages with the hub sleeve 11, is formed on its back face, i.e., inner circumference with taper surfaces 12 and 13 which have their radii gradually increased from the two end portions to the central portion, as taken in the axial direction. On the other hand, the synchronizer rings 9 and 10 are formed with radial holes 14 and 15. In these holes 14 and 18, there are movably received balls 16 and 17 acting as inertial masses. These balls 16 and 17 are carried radially outward by the centrifugal force.
In the synchronizer rings 9 and 10, as located at the sides of the spline pieces 5 and 6 so that they are not engaged by the hub sleeve 11, therefore, the balls 16 and 17 are carried radially outward by the centrifugal force to move toward the axial center along the taper surfaces 12 and 1S of the clutch hub 2. As a result, the synchronizer rings 9 and 10 are urged away from the spline pieces 5 and 6 so that the slip is eliminated at the taper cone portions 7 and 8.
In the synchronizer of the prior art described above, the centrifugal force to act upon the balls 16 and 17 is converted into axial forces by the taper surfaces 12 and 13 so that the synchronizer rings 9 and 10 may be returned by the axial forces. Since, however, the synchronizer rings 9 and 10 holding the balls 16 and 17 are axially movable small parts, the balls 16 and 17 to be held thereby must be small-sized to have a small mass. Moreover, the taper angle of the taper surfaces 12 and 13 to be formed on the clutch hub 2 is difficult to take a large value because the strength of the clutch hub 2 has to be retained. This necessarily reduces the axial forces which can be generated on the basis of the centrifugal force.
As a result, the aforementioned synchronizer of the prior art finds it difficult to generate axial forces sufficient for returning the synchronizer rings 9 and 10. Especially the synchronizer having the elastic members for pushing the synchronizer rings toward the spline pieces so as to prevent the chatter is required to have the axial forces capable of overcoming the elastic forces of the elastic members, so that the aforementioned mechanism of the prior art can hardly be adopted in the synchronizer of this kind from the practical standpoint.